CHAPTER IX 

 ROCK CONDITION AT FOUNDRY BROOK i 



Foundry brook is a small stream entering the Hudson at Cold 

 Spring in the Highlands. It drains a rather abnormally large valley 

 bordering Bull mountain, and Breakneck ridge on the east, and its 

 axis is in the strike, of the principal structure of the gneisses which 

 form the chief rock formation of the floor. This valley is in exact 

 line with the course of the Hudson from West Point immediately 

 southward, and its rock formations are similar in character and con- 

 dition. 



There is greater variety of rock composition in this belt, i. e. the 

 Foundry Brook-Hudson river belt, than in any other in the High- 

 lands of similar area. The eastern half of the belt is a typical 

 development of banded gneisses and schists and quartzites belonging 

 to the sedimentary representatives of the Highlands gneiss. Small 

 layers of interbedded limestones are frequent together with serpen- 

 tine, and mica and graphite and quartz schists. In addition along 

 the east bank of the Hudson, they are profoundly modified by 

 crushing and shearing in zones that trend with the formation, i. e. 

 in a direction leading toward and through Foundry brook valley. 



The west side is much less variable and is bounded at the margin 

 by one of the most massive types of the region — the Bull mountain 

 and Breakneck mountain gneissoid granites, which are essentially 

 the same as that of Storm King mountain. 



But additional structures enter Foundry brook valley from the 

 western side at an acute angle with its axis and formational trend. 

 These additional structures are two well marked faults, which cross 

 the Hudson — one along the precipitous southeast face of Crows 

 Nest and the other along the southeast face of Storm King moun- 

 tain. These are the most pronounced escarpments of the whole 

 region. The first one crosses the Hudson between Cold Spring and 

 Bull mountain and in passing northeastward loses much of its in- 

 fluence upon topography and its movement is probably dissipated in 

 that direction. A line from the southeastern face of Crows Nest to 

 the point to be described runs n. 50° e. 



1 Explorations at Foundry brook were done under tlie direction of Mr 

 William E. S-wift, division engineer, now in charge of the Hudson River 

 division of the Northern aqueduct. 



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